The proposed research seeks to obtain information regarding the mechanisms by which mononuclear phagocytes kill or inhibit the intracellular growth of facultative intracellular parasites. An objective of this study is to ascertain whether pinocytosis provides macrophages with a means of utilization of materials present in serum or cells for augmentation or modification of their antibacterial activity. We have shown that macrophages exist in a hierarchy of activation states with respect to their ability to suppress the intracellular growth of certain microorganisms. It will be determined whether pinocytosis is linked to the development of the activated state and/or the expression of antibacterial action of activated macrophages. Experiments will continue to describe the metabolic requirements for the antimicrobial capabilities of macrophages in various stages of activation. The work will further examine whether oxygen dependent killing mechanisms are available to subpopulations of immunologically activated macrophages for the destruction of Listeria monocytogenes and other bacterial species. We will also continue to probe the role of prostaglandin and thromboxane intermediates in the bactericidal process.